The combination of surface-active solid substances with microorganisms to increase the activity thereof in bio-conversion processes is known. By way of example, in accordance with FR-A No. 2,233,334, ion exchange resins are added to enzyme suspensions. The adsorption of cells on, for example, Al.sub.2 O.sub.3, bentonites and SiO.sub.2 and their subsequent embedding in polyacrylates is described in DE-A Nos. 2,633,259 and 2,703,834.
The embedding of cells in polyacrylates or polyurethane gels to improve the handling of the cells in bio-conversion processes is known. DE-A No. 2,629,692 describes the embedding in photohardenable resin, such as in polyurethane containing photocrosslinkable acrylate double bonds. Tanaka et al. describe, in the European Journal of Applied Microbiology and Biotechnology 7, Pates 351 et. seq. (1979), a process for embedding complete cells in polyurethane-hydrogel. The cells which are not capable of growth display, in an immobilized state, enzymatic activity in bio-conversion processes. The embedding of cells which are optionally capable of growth in polyurethane-hydrogels is described in DE-A No. 2,929,872.
The hitherto known combinations of surface-active substances and cells, which were optionally also embedded in gels, were not suitable for purifying waste water or outgoing air in a simple and effective manner.